[gitaarik]

Server? I never encouter that while using tmux.

You can just use one session if you like, and if you do, it's the default, so you don't have to do anything special.

Tabs and Windows work similar as in screen as far as I can see.

[remram]

No, you can't. Using one session, every client have to show exactly the same panels with the same layout in the same terminal size.